O'Fallon Water Hardness & Quality Report (2026)

The City of O'Fallon Water and Sewer Department serves approximately 13,000 customers in St. Charles County, Missouri. The primary source is a 6.0 million-gallon-per-day reverse osmosis/membrane water treatment plant fed by five alluvial wells, supplemented by four deep wells. The system includes three booster pump stations, four elevated storage tanks, three ground storage tanks, and over 170 miles of distribution lines. O'Fallon also purchases treated water from St. Charles County Public Water Supply District 2 and St. Louis City Public Water Supply, whose plants process Missouri River water.

Local wells tap the Mississippi Embayment aquifer system, drawing from alluvial sands and gravels overlying Paleozoic limestone formations including the Kimmswick Limestone and Plattin Group. Pleistocene glacial deposits and Holocene sediments in the Mississippi River Valley allow high infiltration, dissolving substantial calcium and magnesium from carbonate bedrock. Purchased surface water from the Missouri River watershed carries additional dissolved solids from upstream Paleozoic limestone terrains, blending with karst-influenced groundwater for a consistently very hard mineral profile.

Very hard water promotes significant scale buildup in pipes, water heaters, dishwashers, and washing machines, reducing efficiency and lifespan. White deposits on fixtures and reduced soap lathering are common. Regular descaling, sediment filters, and vinegar soaks for faucets help mitigate effects, but a water softener is strongly recommended to prevent damage and improve cleaning performance. pH at entry is maintained at 7.1–7.5; bromochloroacetic acid has been detected above health guidelines in some tests, and the 2025 Consumer Confidence Report confirms compliance with microbial, lead, and copper standards.